Liquid crystal display panels of lateral electric field modes, such as the In-Plane Switching (IPS) mode or the Fringe Field Switching (FFS) mode, have the advantage of smaller viewing angle dependence of γ (gamma) characteristics than in conventional liquid crystal display panels of vertical electric field modes (e.g., the VA mode). This has led to their use as medium- to small-sized liquid crystal display panels in particular.
On the other hand, as liquid crystal display panels increase in resolution, their pixel aperture ratio (i.e., a ratio of the total area of pixel apertures to the display region) becomes smaller, thus making it difficult to obtain sufficient display luminance. Of particular problem is the decrease in the contrast ratio when medium- to small-sized liquid crystal display panels for mobile applications are observed in a bright environment, e.g., outdoors.
A conventional remedy has been to increase the backlight luminance in order to enhance the display luminance, thus improving the contrast ratio. However, an increased backlight luminance induces a problem of increased power consumption, and thus any remedy that is based on increased backlight luminance has come near its limit.
One cause for the decreased contrast ratio of a liquid crystal display panel in a bright environment is reflection by the liquid crystal display panel. Accordingly, attempts have also been made to improve the contrast ratio by suppressing reflection by the liquid crystal display panel.
For example, Patent Document 1 discloses a liquid crystal display panel of the IPS mode, in which a phase plate (which may also be referred to as the “front phase plate”) is provided between a linear polarizer (which may also be referred to as the “front linear polarizer”) that is disposed on the viewer's side (which may also be referred to as the “front” side) and a liquid crystal cell, thus restraining light which has been reflected by the liquid crystal cell from going out to the viewer's side. The front phase plate is designed so that linearly polarized light which has been transmitted through the front linear polarizer becomes circularly polarized light that rotates in a first direction and enters the liquid crystal cell. In other words, the front linear polarizer and the front phase plate together function as a circular polarizer. When circularly polarized light is reflected (at an interface where the refractive index changes from small to large), a phase shift by n radians occurs in both the P wave and the S wave, whereby the direction of rotation is inverted. As a result, light which has been reflected by the liquid crystal cell (transparent substrate) becomes circularly polarized light whose direction of rotation is a second direction (being opposite to the first direction), and this circularly polarized light passes through the front phase plate to be converted into linearly polarized light, which is absorbed by the front linear polarizer.
The liquid crystal display panel of Patent Document 1 further includes a phase plate (which may also be referred to as the “rear phase plate”) being disposed between a linear polarizer (which may also be referred to as the “rear linear polarizer”) that is disposed on the backlight side (which may also be referred to as the “rear” side) and the liquid crystal cell. The rear phase plate is designed so that, when linearly polarized light that has been transmitted through the rear linear polarizer passes through the rear phase plate and the liquid crystal layer in a black displaying state, it becomes circularly polarized light whose direction of rotation is the second direction, which is opposite to the first direction. When circularly polarized light whose direction of rotation is the second direction passes through the front phase plate, it is converted into linearly polarized light, which is absorbed by the front polarizer. According to Patent Document 1, a liquid crystal display panel of the IPS mode is obtained which can provide a good image quality even in outdoor use.